The present invention relates to the mounting of antennas, and more specifically to the mounting of an automotive antenna to provide an RF contact to the vehicle roof.
Antennas have been used on automobiles for many years. Originally, antennas were installed on automobiles to allow for reception of signals for the car radio. A whip antenna protruding from one of the vehicle fenders for radio reception was standard on most automobiles. Later, antennas that were either embedded within or affixed to the inside of the windshield of the automobile were developed. These in-glass or on-glass antennas ran around the perimeter of the windshield and were less visible than the whip antennas and less susceptible to damage from external elements such as weather or vandalism.
Today, complicated on-board communication systems are used in the automotive industry. Vehicle manufacturers offer systems with features such as built in telephone communication and global positioning satellite (GPS) systems. With the introduction of these complex systems, there was a corresponding increase in the complexity of the antennas required. These systems require antennas that can both receive and transmit signals on several frequency bands. The Personal Communication Service (PCS) band and the Advance Mobile Phone Service (AMPS) band are the most common frequency bands used in cellular telephone communication, with the PCS band used primarily for digital transmissions and the AMPS band used primarily for analog transmissions. Global positioning satellite systems operate within a third distinct frequency band known as the GPS band.
Several types of antennas have been used in conjunction with these kinds of communication systems. Patch, dipole and slot antennas are examples of well known types of antennas used in such applications. The predominant mode of reception for these systems is vertical polarization. Single pole and dipole antennas provide polarization in the same direction as the orientation of the antenna, while slot antennas provide polarization perpendicular to the orientation of the antenna. For example, a standard single pole or dipole whip antenna would need to be vertically oriented to achieve the desired vertical polarization. A slot antenna would need to be horizontally oriented to provide the desired vertical polarization. Vertically oriented whip antennas have been used on the rooftop, fenders, and rear windshield of vehicles for mobile telephone reception for several years.
External vertical whip antennas have several disadvantages. First, they are not aesthetically desirable. Also, they are easily susceptible to damage from external forces such as weather, vandalism, and automatic car washes. There exists a desire among vehicle designers to remove the external whip antennas and replace them with on-glass antennas in a manner similar to what had been done previously for radio reception.
On-glass antennas for the complex communication systems used today created a new set of problems. Patch antennas were commonly used because of their small size. However, patch antennas are sensitive to the placement of the antenna relative to the vehicle sheet metal. Placing the antenna close to the roof panel of the vehicle detunes the antenna from the desired center frequency, changes the gain characteristics, and shifts the radiation pattern.
To overcome these problems, it was observed that, by coupling the antenna to the roof panel of the vehicle, the undesirable tuning effects could be minimized. This phenomena is the subject of U.S. Pat. No. 5,959,581 issued to Fusinski, which is incorporated fully herein by reference.
As shown in FIG. 1, coupling of the on-glass antenna unit 101 (mounted to the windshield 107) to the roof panel 105 has been achieved by attaching a thin strip of copper or brass metal 103 to the roof panel 105 at one end and to the antenna unit 101 at the other end. The metal strip 103 was affixed to the roof panel 105 by either soldering or using a pressure sensitive adhesive. This technique provided the benefits associated with coupling the antenna to the roof panel; however it created several drawbacks from a manufacturing standpoint. The installation of the coupling strip proved to be a labor intensive operation. Because the coupling strip 103 was attached to the mounted on-glass antenna unit 101 at one end and the roof panel 105 at the other end, it could not be installed until after the windshield 107 was installed into the vehicle. Thus, the antenna installation required the antenna to be installed in the assembly plant after the windshield installation but prior to the installation of the interior trim components such as the vehicle headliner and moldings. Alternatively, the antenna could be installed as an aftermarket item; however, later installation required the vehicle headliner to be pulled back to contact the conductive strip to the roof panel. This would then require the headliner of the vehicle to be reinstalled.
Another shortcoming with aftermarket installation was that often the adhesive or solder used to install the conductive strip would accidentally come in contact with the headliner. When this would occur, the vehicle would need to have the headliner replaced. This is usually a task that required the vehicle to be returned to the factory where the windshield and headliner were installed.
It is desired to be able to eliminate the coupling strip and the various installation problems associated with the conductive strip, while at the same time maintaining the advantages that are derived from an RF grounding of the antenna unit to the vehicle roof.
It is further desired that the antenna could be mounted to the windshield prior to the installation of the windshield in the vehicle, or that the antenna can be mounted in the vehicle after the windshield glass has been installed without requiring any disassembly of the installed headliner, and in such event, that the antenna unit can be mounted at this stage without using any glues or epoxies that could cause damage to the installed headliner.
The present invention provides an improved method for creating an RF ground from a glass mounted antenna to the roof panel of an automobile. It provides for a conductive RF path to the roof panel of the vehicle via a grounding path extending on the glass surface from the antenna unit to the roof panel. The grounding path on the vehicle glass is created prior to the installation of the windshield in the vehicle.
In a preferred embodiment, the conductive path is created by applying a conductive fret to the inside of the windshield glass. The windshield is installed into the vehicle using a carbon-loaded epoxy, which is a well known method of installing windshields into automobiles. Because of the properties of the epoxy, an RF contact is created between the conductive fret on the windshield and the roof panel of the vehicle. The antenna is mounted to the vehicle windshield using a high bond adhesive such as a very high bond (VHB) double-sided tape. When the antenna is mounted, a conductive gasket is compressed between a contact area on the antenna unit and a contact area on the conductive fret on the windshield glass, creating a conductive path from the antenna, through the conductive gasket, along the conductive fret, to the top edge of the windshield and to the roof panel via the RF conducting epoxy used to install the windshield. This provides a complete RF ground path from the antenna to the vehicle roof.